1. Field of the Invention
The present invention relates to a fuel cell including cell units each formed by stacking an electrolyte electrode assembly and a metal separator. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes. A plurality of fluid flow fields are formed in each of the cell units for allowing fluids of a fuel gas, an oxygen-containing gas, and a coolant to flow along electrode surfaces.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (electrolyte electrode assembly) (MEA) which includes an anode, a cathode, and a solid polymer electrolyte membrane interposed between the anode and the cathode. The solid polymer electrolyte membrane is a polymer ion exchange membrane. Each of the anode and the cathode includes an electrode catalyst layer and a porous carbon layer. The membrane electrode assembly and separators (bipolar plates) sandwiching the membrane electrode assembly make up a unit cell. In use, generally, a predetermined number of unit cells are stacked together to form a fuel cell stack mounted in a vehicle.
In general, mostly, the fuel cell adopts so called internal manifold structure where a fuel gas supply passage and a fuel gas discharge passage as passages of a fuel gas, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage as passages of an oxygen-containing gas, and a coolant supply passage and a coolant discharge passage as passages of a coolant extend through the cell units in the stacking direction.
Therefore, in the separators, a plurality of fluid passages, i.e., the fuel gas supply passage, the fuel gas discharge passage, the oxygen-containing gas supply passage, the oxygen-containing gas discharge passage, the coolant supply passage, and the coolant discharge passage are provided. Thus, the area of the separators is considerably large. In particular, in the case where metal separators are adopted as the separators, the amount of expensive material such as stainless steel used for the separators is increased, and the unit cost of the part becomes high.
In this regard, for example, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2009-009838, electrolyte electrode assemblies and metal separators are stacked, each of the electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes, and a resin frame is provided at the outer end of the electrolyte electrode assembly. Fluid passages extend through the frame, and the metal separator is positioned inside the fluid passages.